The invention relates to a chemical mechanical polishing (CMP) process which is used for flattening an insulated layer embedded in a trench and an interlayer dielectric in a multi-layer wiring process, in particular relates to a dresser which makes it possible to dress and condition a polishing pad surface deteriorated by polishing treatment, and a method for dressing a polishing pad by using this dresser.
Hitherto, the CMP process used for a semiconductor apparatus has been used for flattening a thin layer, for example, an insulated layer or a metal layer formed on a semiconductor wafer by CVD or the like.
The CMP process is a process for making a thin layer on the surface of a semiconductor wafer flat by infiltrating a polishing material containing polishing particles, which is referred to as a slurry, into a polishing pad set up on a polishing plate and rotating the polishing pad accompanied with rotation of the polishing plate to polish the semiconductor wafer with the rotating polishing pad. Polishing many wafers by this process, i.e., carrying out polishing treatment of wafers many times, results in a problem that the surface of the polishing pad becomes rough to be deteriorated. Hitherto, surface-treatment, referred to as dressing, has been conducted, in order to restore the rough surface to the initial condition thereof as much as possible.
In the CMP process which is used for manufacturing a semiconductor apparatus, polishing is carried out under a condition that a polishing material is present between the polishing pad and the semiconductor wafer. A material for the polishing pad used for polishing includes various materials. A material which is commonly used is a polyurethane foam. The polishing pad composed of the polyurethane foam has in the surface thereof a large number of fines bores, and keeps a polishing material in the bores to enable polishing. However, if the polishing treatment of a semiconductor wafer is conducted many times in application of the CMP process to manufacture a semiconductor apparatus, reaction products and particles of the polishing material are gradually pressed against the inner portions of the bores so that they are confined into the bores. Polishing under such a condition causes a polishing rate and uniformity from polishing to be decreased.
When the urethane foam is used for the polishing pad, an initial treatment is necessary which is for making the surface of the polishing pad rough to some extent at the start of use of the pad and which is called conditioning. Making the surface rough by this treatment is indispensable for obtaining a stable polishing rate and uniformity from polishing.
It is known that the polishing pad is remarkably deteriorated by adding, into the polishing material, a material having a high viscosity such as a high molecular surfactant or a polysaccharide besides polishing particles. Attention has been paid to a serious problem that use of such a deteriorated polishing pad causes drop in a yield rate in the CMP process for a semiconductor device wafer in which fine patterns are formed at a high density.
Hitherto, treatment for setting a pad, which is referred to dressing, has been conducted to remove off an alien substance with which the bores are blocked and scrape off a rough surface of the pad. For the dressing, there is usually used a diamond dresser in which diamond particles are incorporated into a resin or on which diamond particles are electrodeposited. The diamond dresser makes it possible to remove off the alien substance substantially completely because of scraping off the surface layer of the polyurethane foam; however, it causes the surface state of the polishing pad to be returned to the surface state before being subjected to the initial treatment. Therefore, unless after the dressing treatment the pad is conditioned to make the surface thereof rough, it is impossible to reproduce a stable polishing rate and uniformity form polishing. A silicon wafer may be used for the conditioning. Specifically, the polishing pad may be conditioned by polishing the silicon wafer with the polishing pad for about 60 minutes, i.e., the dummy-polishing treatment with the silicon wafer. Much time is spent on the dummy-polishing treatment with the silicon wafer. Consequently, hitherto a decline in productivity in this process has been a serious problem.